1. Field of the Invention
The present invention relates to an optical element apparatus used in an optical information recording and retrieving apparatus for optically recording on and retrieving information from an information recording medium.
2. Description of the Related Art
Coarse and fine actuators are required in recording on or retrieving information from an optical information recording medium, such as an optical disk. The coarse actuator is used to coarsely drive an optical element in a tracking direction for an access to a track. The fine actuator is used to finely drive the optical element in a focusing direction and the tracking direction, in order to apply a beam spot properly. Conventionally, these coarse and fine actuators must be provided with their respective magnetic circuits. Disclosed in Published Unexamined Japanese Patent Application No. 59-135638, however, is a newly developed optical element drive apparatus. According to this apparatus, the magnetic circuits are used in common to the actuators, so that the size and weight of the apparatus are reduced. Referring now to FIGS. 1 and 2, this drive apparatus will be described in brief.
The optical element drive apparatus comprises a pair of permanent magnets 71 and 72, which extend parallel to each other so as to form translational paths, and a pair of supporting iron rods 73 and 74. A magnetic gap 75 is defined between the magnet 71 and the rod 73, and a magnetic gap 76 between the magnet 72 and the rod 74.
A holder 77 is supported on the supporting rods 73 and 74. A penetrating opening portion is formed on each side of the holder 77. The holder 77 is movably supported on the rods 73 and 74 in a manner such that the rods are loosely inserted in their corresponding opening portions.
An optical element 78 is held in the center of the front portion of the holder 77. A pair of focusing coils 79 and 80 are fixed individually to the opposite sides of the front portion of the holder 77 so that they are situated in the magnetic gaps 75 and 76, respectively. In this arrangement, the focusing coils 79 and 8 is isolated from the optical element 78.
Also, a pair of tracking coils 81 and 82 are fixed individually to the opposite sides of the rear portion of the holder 77 so that they are partially situated in the magnetic gaps 75 and 76, respectively. These tracking coils 81 and 82 are wound around the supporting rods 73 and 74, respectively, with a fine play.
Thus, the focusing coils 79 and 80 for driving the optical element 78 and the tracking coils 81 and 82 for driving the holder 77 are located in the common magnetic gaps 75 and 76.
In the conventional optical element drive apparatus constructed in this manner, the magnetic gaps are formed substantially at the opposite ends of the translational paths, so that the focusing coils are located wide apart from the optical element. Accordingly, the holding member of the optical element is bulky, so that the weight of the apparatus increases, the operating sensitivity is lowered, and the whole pickup is large-sized. Since the opening portions penetrated by the supporting rods are formed in the holding member, moreover, the rigidity and resonance frequency of the holding member are low. Further, the common magnetic gaps are used to drive the optical element and the holding member, so that the coils cannot enjoy their optimum magnetic gaps. Since the magnets are required corresponding to the stroke in the tracking direction, furthermore, the cost of production is high.